Electrical interlock control system



Nov. 10, 1942. c. L. LOOTENS ELECTRICAL INTERLOCK CONTROL SYSTEM Filed Dec. 27, 1940 wukaom NHEQ m e m (M/a551, Laura/5 W WMW Patented Nov. 10, 1942,

2,301,910 ELECTRICAL maamcx CONTROL SYSTEM Charles L. Lootens, North Hollywood, CaliL, as-

signor to Republic Prod 'tion 01' New York uctions, Inc., a corpora- Application December 27, 1940, Serial No. 371,981

- lock, it is necessary that the projectionist" and 13' Claim.

This invention relates to motor control circuits and particularly to control circuits for motion picture apparatus such as cameras, projectors, and the like.

In the art of motion picture production, many so-called process shots are made, these particular shots involving the photographing of a translucent picture screen on the rear side of which there is projected a motion picture. Since both the camera and the projector utilize intermittent pull-down mechanisms and shutters, it is essential that respective elements on both the camera and the projector function synchronously and isochronously. In other words, not only should the films in both the camera and projector be advanced at the same constant speed, but the respective intermittent mechanisms and shutters should have the same constant phase relationship.

In systems of this type the camera and projector motors are started and run in electrical interlock. Such motor drive systems are well known and usually employ a synchronous motor for driving a distributor or alternating current generator which supplies the interlocking power to the rotors of the camera and projector 'motors. The motors and distributor are first locked in a certain electrical position by energizing one phase of the three-phase circuit to the stators oi the distributor and load motors. This connection adjusts the rotors of the load motors to a position depending on that of the rotor of the distributor and in accordance with the number of poles on the distributorand respective motors. The other two phases of the circuit are then energized and the load motors come up to speed in step with the rotation of the rotor of the distributor. In the past, when such systems were used for driving the projector and camera for a processshot, the cameraman and projectionist communicated with one another and adjusted their respective shutters to the same position after the motors had been electrically interlocked. The adjusting mechanism usually included a clutch between the motor shaft and film driving mechanism, one such type of clutch system being disclosed and claimed in U. S. Patents 1,980,- 806 of November 13, 1934, and 2,004,992 of June 18, 1935.

In the use of interlock drive systems for motion picture cameras and projectors, the motors thereof generally have a speed diflerent from that of the shutters whose speed is fixed at 1440 R. P. M.. Since these motor speeds are usually 1200 R. P. M.. gears are required between the motor and shutter shafts of a ratio such as 6-to-5. However, since the distributor rotor may assume an infinite numbenoi stopping positions, it is obvious that the rotors oi. the motors may have a similar number of locking positions. It will be appreciated, therefore, that after each intercameraman adjust their shutters with respect to the lock position of the rotors or their respective motors. Now, it the rotor of the distributor always had a predetermined position at interlock, the number of rotor positions for the motors would be materially limited.

The present invention is directed to a system which automatically adjusts the distributor rotor to a predetermined position with respect to its stator immediately subsequent to the disconnection of the distributor, its driving motor and the load motors from the power source. The adjusting mechanism is completely automatic and it is only necessary for the operator to throw the stop switch to immediately set in motion the adjusting mechanism. The adjusting mechanism operates in two steps so that regardless of the stopping position of the distributor rotor, it will be rotated to the predetermined position and then stopped at exactly that point. Should the stopping position be near to the predetermined position, electromagnetic means are energized to slightly rotate the rotor to the exact position desired. Should the stoppingposition be beyond the limits of control of the electromagnetic means, power is first supplied to the distributor windings to rotate the motor to within these limits, after which power is supplied to the electromagnetic means to accomplish the final positioning. The principal object of the invention, therefore, is to improve the operation oi interlock motor drive systems for motion picture apparatus.

Another object of the invention is to automatically adjust a rotatable element to a predetermined position.

A iurther object of the invention is to automatically adjust the rotor of an interlock distributing generator to a predetermined setting.

A further object of the invention is to facilitate the adjustment of a generator rotor to a predetermined physical position after the rotor has been stopped. 1

A further object of the invention is to automatically rotate the rotor of a generator to a predetermined starting position if the rotor does not stop at the predetermined position.

Although the novel features which are believed to be characteristic of this invention will be pointed .out with particularity in the appended .claims, the manner of its organization and the be better understood mode of its operation will by referring to the iollowing description read in conjunction with the accompanying drawing forming a part thereof, in which the single figure is a diagrammatic-schematic drawing embodying the invention.

Referring tothe drawing, a three-phase-driving motor 5 or any conventional type is shown mechanically connected to a distributor-generator 5, an electromagnetic brake 'I being positioned on the connecting shaft. The brake 1 is applied when deenergized and is released when energized. Mounted on extension 8 of the distributor shaft are two electromagnetic coils i and H having iron cores, as shown by the dotted lines. Mounted on the end of the shaft 8 and adapted to rotate therewith is a three-slip-ring disc unit l3 having a copper inner ring l4, an intermediate copper ring i and a copper segment i5, all oi which are insulated from one another. The rings i4 and i5 are continuous, while only the seg ment i5, which extends over approximately onetwentieth of the circle, is conducting, the remaining portion l1 of this ring being composed of non-conducting material.

Respective brushes i9, and 2| contact the three rings. The brush is connected to an electromagnetic coil 23 having an iron core, as shown by the dotted lines, and then to a similar coil 24, these coils being stationary except that they may be adjusted to change the stopping position of the shaft 8. It will also be noted that the conducting segment I5 is permanently connected to the inner ring H by connection 33, while the inner ring I4 is connected to rotatable coil II in series with the rotatable coil l5 and middle ring l5, and that the brush l9 contacts the inner ring |4. Thus, if a source of electrical potential were connected to brush l9 and to coil 24, the four coils would be energized over a circuit from brush l9, inner ring i4, coils H and I0, intermediate ring l5, brush 2|) and coils 23 and 24.

If we now refer to relays B and D, it will be noted that direct current may be supplied to the coils H), II, 23 and 24 from one terminal of a direct current source connected at 25, over conductor 21, contact 28 when closed, conductor 29, through the brush and ring circuit just traced, then over conductor 32, contact 34, when closed, and over conductor 35, to the other terminal of direct current source 25. Thus, with the relays B and D energized, it will be observed that direct current voltage will be impressed upon the coils IO, M, 23 and 24, energizing these coils and producing an attraction between their respective cores to position and hold the shaft 8 in the position shown in the drawing. To obtain this attraction, the adjacent poles of the cores are given opposite polarities. The energizing circuit is only possible, however, with both of relays B and D energized.

Although the energization of relay B will be explained later, the energization of relay D is under control of brush 2| and segment l5. With the brush 2| on the segment l5 and contact 25 of relay B closed, a circuit is completed from DC source 25, over conductor 21, contact 28, conductor 29, brush i9, ring i4, connection 33, segment i5, brush 2|, conductor 3|, coil of relay D, and conductor 35 to source 25, This circuit energizes relay D, closing its contacts 35 and 34, the closing of contact 34 energizing the coils In, H, 23 and 24, as described above. The closing of contact of relay D will hold this relay energized over a circuit connected between conductors 29 and in case the segment passes beyond the brush 2|. It is to be noted that a relay E has its winding connected in parallel with the winding of relay D and is thus simultaneously energized and held energized in the same manner as relay D. The purpose of relay E will be described hereinafter. Thus, with the shaft 8 in such a position that the brush 2| contacts the segment i5, the relay D is energized, in which case the fixed and rotatable coils will be energized and will be so positioned that their energization will permit them to rotate the shaft 8 to a vertical position, as shown, or in any other position in accordance with the adjustment of fixed coils 23 and 24. It will be noted that segment I5 is so located that its center is in line with the axes of coils H), II, 23 and 24.

The portion of the circuit above-described is for the purpose of a vernier adjustment of the shaft 8 after the shaft 8 has been rotated to the point where the brush 2| contacts the segment i5. Since this segment is of a length extending over approximately an 18 angle, the rotatable coils will always be close enough to the fixed coils before energization to come within the field of attraction and assure their locking the shaft 5 in a single position. Thus, with the relay B energized and contact 28 closed, energy will be supplied to the relay D, operating this relay, which will close its contacts 35 and 34, one of which holds the relay energized, and the other of which energizes the four positioning coils |5, 23 and 24.

Referring now to the remainder of the circuit, it will be observed that the system is supplied from a three-phase power source over a main switch 40 when closed, this switch connecting the source to three main conductors 4|, 42 and 43. The driving motor 5 is connected to the conductors 4|, 42 and 43 over contacts 48, 49 and 55 when closed, and conductors 5|. Connected across two of the conductors 5| is a pair of conductors 52 for energizing the brake 1, which releases it. Running from the stator of the distributor-generator 5 is a plurality of conductors 54, one of which is connected by a conductor 55 to a contact 55 of a relay L, and the other two of which are connected to contacts 51 and 58 of a relay J. The three conductors 54 are also connected to contacts 58, 5| and 52 01' a relay I and also over three conductors 54 to contacts 55, 55 and 51 of a relay C. It will be observed, therefore, that the stator of the distributor-generator 5 will be supplied with power from the main line conductors 4|, 42 and 43 over contacts 55, 51 and 58 when relays J and L are energized to close these contacts, conductors 59, 18 and 1| connecting the main conductors to the contacts 55, 51 and 55, respectively.

The rotor of the distributor-generator 5 is connected over three conductors 13 and 14 to contacts 15, 11 and 18 of relay I, these last-mentioned contacts also being connected over conductors 55 to the rotor of the load motor 45 and over conductors 5| to the rotor of load motor 45. Thus. the closing of contacts 15, 11 and 18 will interconnect the rotor of the distributor-generator 5 with the rotors of the load motors 45 and 45. To supply the stators of the load motors 45 and 45 with power, contacts 55, 5| and 52 are closed in addition to contacts 55, 51- and 55, which energizes the load motor stators over conductors 82 to the stator of load motor 45 and conductors 83 to the stator of load motor 45. Thus, to energize the motor 5, the stator of distributor-generator 5 and the stators of load motors 45 and 45, the relays I, J and L must be energized. The motor 5 is then supplied with power over contacts 48, 48 and 55, the stator of the distributor-generator 5 supplied over contacts 55, 51 and 58, and the stators of load motors 45 and 45, over contacts 55, 51 and 58 and contacts 55, 5| and 52. The energization of relay I also connects all the rotors of the distributor-generator and load motors together over contacts I8, 11 and I8.

Thus, with the power switch 48 closed and the relays I. J and L energized, the motor interlock system will be started and run. Since it is well known that in operating such a system, one phase of the stators of the distributor-generator and the motors are first energized, it will be observed that the operation of only relays I and J will accomplish this result, since only contacts 81 and 88 will be closed. The energization of only these relays is accomplished by a lock switch 88, which closes contacts 81, 88, 80, 8|, 82, I8, 11 and I8. After the motors and distributor-generator have been locked, a run switch 81 is momentarily closed, energizing relay L, which will close the other two phases of the stators of the distributorgenerator and motors over contact 88, and will also close the power circuit to the motor 8 over contacts 48, 49 and 80.

The system so far described includes the direct current portion for obtaining the exact positioning of the shaft 8 and the locking and running circuits for the motors. The automatic control portion of the system for relays I, J and L and the rotation of unit I8 so that segment I8 contacts brush 2I after the motors have been stopped will now be described. Tapped oil from main conductors 4| and 42 is a pair of conductors 89 and 80 having a pair of fuses 9i therein and a 3 momentarily-opening stop switch 92. Since switch 92 is normally closed at all times, a circuit may be traced from power conductor 89 through the coil of a relay A, conductor 84, swinger 98 of a relay G, and over conductor 98 to power conductor 80. This circuit will energize the coil of relay A, which closes its contact IOI. The relay A is of the slow-to-make typ utilizing a dashpot 98 to accomplish the delay action. The purpose of this delayed action will be explained later.

The closing of contact IOI energizes relay B over a circuit extending from power conductor 88, contact IOI, conductor I02, the coil of relay B, conductor I08, conductor 98 to power conducter- 80. Th energization of relay B closes its three contacts 28, I08 and I08, the closing of contact 28 connecting the direct current source at 28 to the coils I0, II, 28 and 24 it the brush 2I is upon segment I8. If the brush is not on segment I8, the relays D and E remain open, as explained above. However, the energization of relay B, through the closing of contact I08, energizes the brake I, releasing it.

The closing of the third contact I08 of relay 8 energizes relay C over an energizing circuit from power conductor 89, contact I M, conductor I02, conductor I08, back contact I09 of relay E, conductor IIO, closed contact I08, conductor III, the coil of relay C, conductor I I2, conductor I08, conductor 98 to power conductor 90. The energization of relay C is for the purpose of energizing the distributor-generator 8 and this unit only. It will be noted that the three-phase conductors H, 42 and 43 are connected to contacts 88, 88 and 81 of relay C, over conductors H4, and with these contacts closed, the stator of the distributor-generator is energized over conductors II4,

- contacts 85, 88 and 81, conductors 84, and conductors 84. The stators of load motors 48 and 48 will not be energized, however, because contacts 80. M and 82 of relay I are not closed. Simultaneously with the closing of contacts 88, 88 and 81. contacts II8, III and H8 are closed.

the rotor windings of th distributor-generator 8 through a plurality of ballast resistance lamps I20 over conductors I8 so that the rotor of the distributor rotates slowly. Thus, the energization of relay 0 will energize the distributor-generator only and will start the shaft 8 rotating. The shaft 8 will continue to rotate until the brush 2I contacts the segment I8, and when this contact is made, the relays D and E will be energized, as explained above, and direct current energy will be supplied to the coils I0, II, 28 and 24. The energization of relay E breaks the holding circuit for relay C at contact I08 and power is removed from the distributor 8.

Upon the energization of the relay 0!), the swinger of the relay moves to its front contact I22, which completes a new circuit as follows: This new circuit is from power conductor 89, over contact IOI, conductor I02, conductor I08, contact I22, conductor I28, to a point I24 where the circuit divides. one portion going through the coil of a relay 1'' and over conductor I 28 to power conductor 90, and the other 'over the coil of relay G and conductor 88 to power conductor 80. This circuit immediately energizes relays F and G, and the swinger of relay F immediately closes its contact I21, the closing of which looks the relay F over a circuit from power conductor 89, conductor I28, contact I21, conductor I29, the winding of relay F, conductor I28, to power conductor 90. Although relay G was energized at the same time as relay F, this relay is of the slow-to-break type of relay wherein there is a delay period after energization and before its swinger 95 breaks contact at- I8I. Although this relay may be of any well known type, it is represented herein as having a dashpot I84 and a spring I85 so that I immediately upon energization, the piston starts The closing of these three contacts short-circuits moving to the left but will not move the swinger 95 until it has taken up the tension in the spring I88. A relay known as the General Electric timedelay relay CR-7504-A1A is satisfactory for obtaining the slow-to-break action. The purpose of this time delay at this point is to permit relay D to remain closed and the coils I0, II, 28 and 24 to remain energized long enough to accurately position the shaft 8 since there may be a slight hunting action before the shaft 8 becomes stationary.

Upon the breaking of the A is deenergized over the which deenergizes relay B, which, in turn, deenergizes relays D and E. The making of contact I82 of relay G, however, energizes a relay'H from power conductor 90, over conductor 98, swinger 95 of relay G, contact I82, conductor I 81, the coil of relay H, to the power conductor 89. The energization of relay H will close its contact I89, and this contact will remain closed since relay G is locked up over the locked contact I21 of relay F. The closing of contact I39 will extend power to relays I, J, K and L over conductor and conductor I40.

As mentioned above, relays I, J and L control the locking and starting of the system. Thus, with contact I89 of relay H closed, these relays may now be energized. The closing of lock switch 88 previously described, energizes relays I and J over conductors 90, I40 and I. Start or run switch 81 is a momentary type of switch, open at all times except when pressed, and the closure thereof energizes both relay L and a relay K, the latter being a holding relay for relay L when the switch 81 is open. Relay K locks itself and contact I9I, the relay circuit first traced,

relay L over its contact I42 and conductors I44 and I45 connected to conductors 80 and I". Thus, with lock switch 86 permanently closed and after the momentary closing of switch 81, all the relays I, J, K and L will remain closed as long as there is voltage on conductors 90 and I40. The power may be removed from these conductors, however, by the momentary opening of stop switch 92 which starts the stopping cycle now to be explained.

The momentary opening of stop switch 92 deenergizes a group of relays. First, relays I, J, K and L are deenergized since the power is removed from conductors 80 and I40. Relays G, F and H are likewise deenergized, the swinger 85 of relay G being permitted to make its back contact at I3l. The opening of contact I39 of relay H breaks one of the power conductors to relays I, J, K and L so that when the switch 92 is closed, these relays will remain deenergized. Under these conditions the motor 5, distributorgenerator 6 and load motors 45 and 48 will come to a stop, brake 'I being applied to the motor 5 and distributorgenerator 6, since the power is removed from conductors 52.

Now assuming that the stopping position of the shaft 8 of the distributor-generator 6 is such that the segment I6 is not in contact with brush 2|, certain of the relays will be operated as traced above, this cycle, in brief, being as follows: With the swinger 95 of relay G on contact I3l, relay A is energized. Relay A is a slow-to-make relay, the purpose of the delay being to permit the ro tating rotor of the distributor-generator to come to a complete stop. If relay A closed its contact immediately upon the operation of stop switch 92, the contact I06 of relay B would close, releasing the brake I. When contact IIII of relay A does close, however, relay B is energized, which, in turn, energizes relay C. The energization of relay C impresses power upon the distributorgenerator and starts the shaft 8 rotating until the brush 2| contacts the segment I8. At this point, relays D and E are energized, these relays being locked in position and connecting direct current to the coils III, II, 23 and 24 to position the shaft 8 at an exact predetermined point. Energization of relay E deenergizes relay C, disconnecting the power from the distributor-generator 6. The energization of relay E also energizes relays G and F, the energlzation of relay F locking this relay and relay G.

After a predetermined delay period to permit shaft 8 to become stationary, relay G operates to break its contact at Ill and make contact at I32. The breaking of contact at I3I deenergizes relay A, relay B and relays D and E. The breaking of contact I06 applies the brake I to the distributor rotor. The making of contact I32 of relay G energizes relay H, closing contact I39 and providing power to relays I, J, K and L when the locking switches 86 and 81 are closed. The system will remain in this condition until the power switch 80 is opened, when all relays are deenergized. When the power switch 40 is again closed, the system will go through the following cycle and relays G, F and H will lock up. It is desired that this positioning cycle be gone through each time the power switch 40 is closed in case the shaft 8 has been displaced from its predetermined position during disuse of the system. Thus, upon the closing of power switch II, the shaft 8 is immediately brought to the desired starting position before the system may be started and operated.

Should the system stop so that brush II is in contact with segment I5, then the energization of relay B will immediately energize relay E so that relay C will not be energized. Relays G, F

and H will lock up, however, readying the system for the interlock and starting operations.

The above system has been used for driving the motors of a process projector and camera and has been found to operate satisfactorily at all times. Its use has avoided substantially all the preliminary adjustments formerly required in making process shots. The invention, of course, eliminates the services of a man to turn the distributor rotor to a predetermined position at the end of each take. Although the invention has been described for driving only two load motors, it is to be understood that more than two motors may be similarly operated with the system.

I claim as my invention:

1. A motor control system comprising a plurality of motors to be started and operated in synchronism, a distributor-generator for controlling the said motors, means adapted to rotate with the rotor of said distributor-generator, said means having attached thereto a pluralityof electromagnetic units, a plurality oi fixed electromagnetic units adapted to interact with said rotating units for positioning the shaft of said distributor-generator in a predetermined position, and a plurality of relays adapted to energize only said distributor-generator for rotating said distributor-generator to a predetermined point, said relays subsequently disconnecting said distributor-generator and energizing said electromagnetic devices for positioning said distributor-generator shaft.

2. An interlock motor system having a plurality of load motors and a distributor-generator, comprising a source of power, means for normally energizing said distributor-generator and said load motors from said source, means for deenergizing said distributor-generator and said motors, an electromagnetic holding circuit for said distributor-generator, and a plurality of relays operated when said distributor-generator and motors are deenergized for reenergizing said distributor-generator only and for deenergizing said distributor-generator when said electromagnetic holding circuit is energized.

3. An interlock motor system having a pinrality of loadmotors and a distributor-generator, comprising a source of power, means for normally energizing said distributor-generator and said load motors from said source, means for deenergizing said distributor-generator and said motors, and a plurality of relays adapted to be operated when said distributor-generator and motors are deenergized ior reenergizing said distributor-generator only, electromagnetic means being provided on said distributor-generator and adapted to be energized when the shaft of said distributor-generator has rotated to a predetermined position and means being provided for deenergizing said distributor-generator when said electromagnetic means are energized.

4. In an electrical interlock motor system, the combination of a plurality of load motors, a distributor-generator, a driving motor for said distributor generator, a source of power, means (or normally connecting said distributor-generator and motors to said power source, a plurality oi serially operated relays, certain of said relays being energized when said distributor-generator and motors are connected to said power supply, and other of said relays being operated when said distributor-generator and motors are disconnected from said power supply, means oper- I ated by said last-mentioned relays for energizing said distributor-generator only, a plurality of electromagnetic means connected to said distributor-generator, and means for energizing said electromagnetic means when the shaft of said distributor-generator is in a predetermined angular position and for deenergizing said distributor-generator.

5. An interlock motor .control system comprising a plurality of load motors, a distributor-generator adapted to be connected to said motors, and a driving motor for said distributor-generator, a source of power, an adjusting circuit for said distributor-generator a plurality of relays adapted to connect said source of power to said distributor-generator, said load motors and said distributor-generator driving motor, another plurality of relays adapted to be energized from said power source during the running of said motors, the energization of said last-mentioned relays controlling the operation of said firstmentioned relays, and a third group of relays adapted to energize only said distributor-generator from said power source after said first-mentioned relays have been deenergized to disconnect said distributor-generator, load motors and driving motor from said power source and to deenergize said distributor-generator and energize said adjusting circuit for said distributor-generator,

6. An interlock motor control system comprising a plurality of load motors, a distributor-generator adapted to be connected to said motors,

and a driving motor for said distributor-generator, a source of power, a plurality of relays adapted to connect said source of power to-said distributor-generator, said load motors and said distributor-generator driving motor, another plurality of relays adapted to be energized from said power source during the running of said motors, the energization of said last-mentioned relays controlling the operation of said firstmentioned relays, and a third group of relays adapted to energize only said distributor-generator from said power source after said first-mentioned relays have been deenergized to disconnect said distributor-generator, load motors and driving motor from said power source, electromagnetic means being provided on the shaft of said distributor-generator, said means being energized after said distributor-generator motor has been rotated to within certain angular limits, and said distributor-generator deenergized.

7. A system for stopping a rotating element at a predetermined position comprising means for rotating said element at a certain speed, means for energizing and de-.-energizing said rotating means, electromagnetic means for adjusting said element to said predetermined position upon energization of said electromagnetic means, means for energizing said electromagnetic means, and means for disconnecting said energizing means for said rotating means when said electromagnetic adjusting means is energized, said energizing means for said electromagnetic means including a commutator adapted to rotate with said element, and a plurality of reiays, one of said relays actuating said disconnecting means, and another of said relays actuating said energizing means for rotating said element, said disconnecting relay controlling the operation of said energizing relay.

8. A system for stopping the shaft of an electromagnetic machine at a predetermined posi tion comprising driving means for said shaft, said shaft also being adapted to be rotated when electrical energy is applied to said machine, means positioned on the shaft of said machine adapted to position said shaft at said predetermined position when said shaft is within certain limits of rotation, means for energizing said machine for rotating said shaft, means for disconnecting said driving means, means for energizing said positioning means, and means for first disconnecting said driving means, then connecting said energizing means for said machine, then disconnecting said energizing means, and then energizing said positioning means.

9. A system in accordance with claim 8 in which means are provided for delaying the energization of said machine a predetermined time after the disconnecting of said driving means.

10. A system for stopping the shaft of an electromagnetic machine at a predetermined position comprising driving means for said shaft, said shaft also being adapted to be rotated when electrical energy is applied to said machine, means positioned on the shaft of said machine adapted to position said shaft at said predetermined position when said shaft is within certain limits oi rotation, means for energizing said machine for rotating said shaft, means for disconnecting said driving means, means for energizing said positioning means, and means for first disconnecting said driving means, then actuating said energizmg means for said machine, and then energizing said positioning means, said last-mentioned means disconnecting said energization means for said machine simultaneously with the energization or said positioning means.

11. A system for-stopping a rotatable element at a predetermined rotational position, a first means for rotating said element at a certain speed, means for energizing and deenergizing said first rotating means, a second rotating means for said element adapted to be energized when said first rotating means is deenergized, means for adjusting and holding said element at said predetermined postion and adapted to be energized when said second rotating means is deenergized, and a plurality of relays for first deenergizing said first rotating means, then energizing said second rotating means and then simultaneously deenergizing said second rotating means and energizing said adjusting means.

12. A system for stopping and looking a rotatable element at a predetermined rotational position, means for rotating said element, means for' energizing. said rotating means, means for holding said rotatable element in said predetermined position, means for locking said rotatable element in said position, and a plurality of relays for first energizing said rotating means and simultaneously releasing said locking means, then deenergizing said rotating means and energizing said holding means, and then deenergizing said holding means and simultaneously actuating said locking means.

13. A system in' accordance with claim 12 in which said holding means includes electromagnets and said locking means includes a brake on said rotatable element adapted to be released when energized and effective when deenergized.

CHARLES L. IDOTENS. 

